Stormwater Management Report 03302026

Water Quality Management As stated previously, since the project does not increase impervious cover by more than 0.25 acres (impervious cover is reduced in the proposed condition), the site does not drain to a water that has a total maximum daily load (TMDL) for TSS reduction, the regulatory requirements of the Code 25-29.4(r) and NJAC 7:8-5.5 are not applicable. Nevertheless, we believe implementation of the project will result in an improvement of runoff quality, when compared to existing site conditions and former use of the property. The anticipated improvement in water quality is based upon the net reduction in impervious cover, as well as a higher percentage of the post-project cover being comprised of mainly roof areas consisting of 44,541 square feet. The NJDEP considers roof runoff “clean,” not requiring TSS removal pursuant to State regulation. Hydrology And Stormwater Management Quantity Control (Peak Flow Attenuation) Estimating runoff rates and volumes for quantity control purposes is done by utilizing what is referred to as the “NRCS Method”, which is also known as the “TR-55” methodology. This is described at length in Chapter 5 of the BMP Manual According to the National Engineering Handbook, as published by the NRCS, the combination of a hydrologic soil group and a land use and treatment class is a hydrologic soil-cover complex, to which a runoff curve number (CN) can be assigned. The CN is an indication of the complex’s runoff potential. The Hydrologic Soil Group(s) for the project site were determined by referencing the NRCS’s Web Soil Survey for the appropriate county. The Time of Concentration, “Tc”, for the existing and the proposed conditions have been calculated through modeling software and the paths are shown on the coverage maps. For the various ground covers, runoff coefficients, “CN”, used in the analysis were 98 for impervious areas such as buildings, parking lot, and walkways, and 71-74 for wooded/landscape areas. The rainfall depths utilized for the project’s design were derived from NOAA Atlas 14, Volume 2, Version 3 point precipitation frequency estimates. An adjustment factor increasing the runoff factor by 1%-6% was applied in per 54 NJR 2187(a) for current storms and another 23% to 46% was added to arrive at a “future” storm intensity. Below is a summary of the storm rainfall depths used for both the existing and

pplied in per 54 NJR 2187(a) for current storms and another 23% to 46% was added to arrive at a “future” storm intensity. Below is a summary of the storm rainfall depths used for both the existing and proposed conditions. Storm 2-year 10-year 100-year Current-Year-2020 3.47 in 5.38 in 9.18 in Future-Year-2050 4.09 in 6.37 in 11.52 in. 5